Risk variables associated with abnormal calcium, magnesium and phosphate levels among emergency department patients.

Objective: The utility of calcium, magnesium and phosphate measurement in the ED is limited. We aimed to determine clinical risk variables for abnormal levels of these electrolytes in order to inform the development of an ordering guideline.

Methods: We performed a retrospective, observational study of patients who presented to a tertiary referral ED between January and June 2017. Adult patients who had serum calcium, magnesium or phosphate tests completed during their ED stay were included. Presenting symptoms and signs, comorbidities, medication use and laboratory values were extracted from the medical record. Patients with missing data items were excluded. Logistic regression models determined clinical risk variables associated with low and high levels of each electrolyte.

Results: A total of 33 120 adults presented during the study period. Of the 1679 calcium, 1576 magnesium and 1511 phosphate tests, 228 (13.6%), 158 (10.0%) and 387 (25.6%) were abnormal, respectively. Significant risk variables (P < 0.05) for abnormal levels were: hypocalcaemia - vomiting, perioral numbness, hand/foot spasm, calcium and phosphate supplements and chemotherapy (odds ratio [OR] range 5.9-17.3); hypercalcaemia - female sex, vomiting, polyuria, confusion, hyperparathyroidism, cancer and type 1 diabetes (OR range 2.3-9.7); hypomagnesemia - female sex, proton pump inhibitor use, tacrolimus use, alcohol abuse and type 2 diabetes (OR range 2.2-13.1); hypermagnesemia - lethargy, thiazide use and chronic kidney disease (OR range 4.3-4.5); hypophosphatemia - nausea, seizure and glucocorticoid use (OR range 1.7-2.1); and hyperphosphataemia - polyuria, diuretics and chronic kidney disease (OR range 1.9-5.0).

Conclusion: A range of demographic, comorbid, medication and clinical variables are associated with abnormal calcium, magnesium and phosphate levels. These findings will inform the development of clinical guidelines to rationalise calcium, magnesium and phosphate testing. Justification may be required for testing patients with no risk variables.